In outline, such an insulator consists of a glass fibre and resin rod sheathed with an elastomer casing which is optionally provided with fins also made of elastomer e.g. EPDM (Ethylene-Propylene-Diene Monomer). One of its ends is fixed to a post via a fitting and its other end has another fitting to which is attached a clip for a conductor.
The rod as a whole and in particular its end which is anchored in the fitting fixed to the post is subjected to high mechanical stresses. It tends to sag under the weight of the conductor; the upper fibres are in reaction while the lower fibres are in compression.
To improve anchoring of the end of the rod, it has already been recommended to machine said end to impart thereto the shape of a single or a double cone; however, it has been observed that under high mechanical loading, racks appear between the fibres in parallel to the fibres.
Preferred embodiments of the present invention mitigate these drawbacks and produce a line post type insulator fixed to a post by anchoring means which impart greater mechanical strength to the rod.